The present invention relates to an anti-locking hydraulic brake system comprising at least one wheel brake and an auxiliary pressure source, with an inlet valve being inserted into the conduit between the auxiliary pressure source and the wheel brake and an outlet valve connected to the return conduit.
A brake system of this type is disclosed, for example, in German patent document DE-OS 36 27 000 which discloses a dual-circuit brake system comprising a tandem master cylinder and a pump for each brake circuit. The wheel brake cylinders, through respective inlet valves, are each in communication with the pressure conduit leading to the pump, and with the brake circuit leading to the master brake cylinder, respectively, and, through an outlet valve, to the return conduit leading to the reservoir. The inlet valve is normally opened, while the outlet valve is normally closed.
During a deceleration process, the rotation of the wheels is permanently monitored. If one of the wheels tends to lock, the pump drive is actuated, and the inlet and outlet valves of the wheel tending to lock are excited such that a pressure is adjusted in the wheel brakes correlating with the optimum slip value of the wheel. For lowering the pressure, the outlet valve is opened and the inlet valve closed, while, for maintaining the pressure, both valves are closed, and, for increasing the pressure, the inlet valve is opened and the outlet valve closed.
The inlet and outlet valves are electromagnetically excited valves comprising a closure member seated on a valve seat. During an anti-locking-controlled deceleration operation, on the valves, a pressure gradient occurs in the brake fluid resulting in control noises causing annoying the driver of the automotive vehicle. It is, therefore, an object of the present invention to substantially decrease the control noises on the valve.